ldap: fix access of non-array

src/www/system_usermanager_import_ldap.php

 <?php
+
 /*
     Copyright (C) 2014-2015 Deciso B.V.
     Copyright (C) 2007 Scott Ullrich <sullrich@gmail.com>
@@ -113,6 +114,7 @@ if ($authcfg['type'] == 'ldap') {
         }
       }
     } else {
+      if (is_array($result)) {
         // list all missing accounts
         foreach ($result as $ldap_user ) {
           if (!in_array($ldap_user['dn'], $confDNs)) {
@@ -122,6 +124,7 @@ if ($authcfg['type'] == 'ldap') {
         ksort($ldap_users);
       }
     }
+  }
 }
 
 include('head.inc');